The present invention relates to disinfection or decontamination of food, water, air and packaging materials, and more particularly, is directed to deactivation or killing of organisms, such as cyst-forming protozoa, such as Cryptosporidium parvum, or viruses, such as poliovirus, in food, water, or air, or on packaging material. Even more particularly, the present invention relates to deactivation of such organisms using high-intensity short-duration pulses of polychromatic light in a broad spectrum.
As used herein the terms "deactivate", or decontaminate and forms thereof refer to the killing or sterilizing, i.e., rendering unable to produce, of microorganisms.
Substantial technical effort has been directed to increasing the levels of microbiological decontamination in water, air, foodstuffs and other microbiologically labile products, and packaging materials so as to preserve these products against microbiological spoilage and/or to prevent infection of their consumers. Such efforts have involved both the treatment of products and packaging material, and the development of packaging techniques for preservation.
The photobiological effects of light, including infrared light (780 nm to 2600 nm; i.e., 3.9.times.10.sup.14 Hz to 1.2.times.10.sup.14 Hz), visible light (380 to 780 nm; i.e., 7.9.times.10.sup.14 Hz to 3.9.times.10.sup.14 Hz), near ultraviolet light (300 to 380 nm; i.e., 1.0.times.10.sup.15 Hz to 7.9.times.10.sup.14 Hz) and far ultraviolet light (170 to 300 nm; i.e., 1.8.times.10.sup.15 Hz to 1.0.times.10.sup.15 Hz), have been studied, and, in particular, efforts have been made to employ light to deactivate microorganisms on food products, containers for food products or medical devices. See, e.g., U.S. Pat. Nos. 4,871,559;
4,910,942; and 5,034,235, issued to Dunn et al. (the '559, '942, and '235 patents), incorporated herein by reference.
Other studies of the photobiological effects of light are reported in Jagger, J., "Introduction to Research in Ultraviolet Photobiology", Prentice Hall, Inc., 1967. U.S. Pat. No. 2,072,417 describes illuminating substances, e.g., milk, with active rays, such as ultraviolet rays; U.S. Pat. No. 3,817,703 describes sterilization of light-transmissive material using pulsed laser light; and U.S. Pat. No. 3,941,670 describes a method of sterilizing materials, including foodstuffs, by exposing the materials to laser illumination to inactivate microorganisms. However, such methods have various deficiencies, such as limited throughput capacity, limited effectiveness in killing microorganisms (particularly, cyst-forming protozoa and viruses), adverse food effects (e.g., negatively affecting food flavor or appearance), inefficient energy conversion (electrical to light) and economic disadvantages.
In the area of water decontamination in particular, heretofore known methods of killing cyst-forming protozoa are in many cases ineffective and inefficient, i.e., overly time consuming or too costly. One commonly used method of water decontamination is the addition of chlorine to water for the purpose of killing microorganisms. Unfortunately, chlorine, at levels that are not also toxic to humans, is ineffective at killing some cyst-forming protozoans. In recent years, for example, outbreaks of Cryptosporidium parvum (C.parvum) have caused illness in hundreds of thousands of people, and have killed numerous others. Such outbreaks are common in the spring and summer rainy seasons when water from feedlots and the like may be undesirably mixed with municipal water supplies. No cost effective method of eradicating C.parvum has heretofore been available.
One attempt to eliminate live C.parvum from water involves exposing contaminated water to ultraviolet light. While limited success has been observed using ultraviolet light and special methods for increasing exposure time or intensity (such as by trapping oocysts in a mechanical filter and exposing the mechanical filter to ultraviolet light) to eradicate low concentrations of C.parvum, i.e., about 2 log cycle reductions, such method requires that the water be exposed to ultraviolet light having an intensity of 15 W/s for more than two hours, i.e., about 150 minutes. Thus, the use of ultraviolet light has proven not to be a viable approach to eradicating C.parvum in municipal water treatment facilities. What is needed is a method of eradicating C.parvum, other cyst-forming protozoa, and other microorganisms, such as viruses, that is both fast, i.e., that can be used practically in a water treatment facility, and that is highly effective, i.e., is effective to deactivate high levels of C.parvum, i.e., more than 2 or 3 log cycles.
In the area of air decontamination, airborne microorganisms, and in particular viruses, and even chemical contaminants, are of major concern. In order to be effective, an air treatment approach must be able to process flowing air as it passes from a contaminated space into an uncontaminated or sterile space. Heretofore, the most common method of air treatment has been to employ micro filters, such as HEPA filters, in a duct in order to physically remove particulate contaminants from the flowing air. Unfortunately, the micro filters employed pose significant impediment to air flow, and therefore require the use of high powered fans and the like in order to pump the air through the air filters. As more particulate contaminants become trapped in the micro filters over time, this impediment to air flow increases. In addition, due to the relatively high resistance to air flow posed by such microfilters, leakage of air around the filters becomes a significant factor in their design. Such filters also are subject to releasing trapped contaminants into the duct when they are removed for replacement and such released contaminants can be subsequently carried by the duct into areas sought to be protected by the filter. Furthermore, some microfilters may be unable to remove particularly small contaminant particles.